Almost everyone can agree that they would like better development, but not everyone can agree what a good site design actually is.To change that, the nonprofit Center for Watershed Protection in 1997 launched a two-year stakeholder process that involved 30 representatives from government agencies, builders groups, professional associations, environmentalists, local planners and others.
The result was agreement on 22 specific Better Site Design techniques that conserve natural areas, save money, reduce pollution and increase property values.
The general goal is to reduce the amount of area disturbed by equipment and covered with pavement, while using creative grading and drainage techniques to reduce runoff and encourage infiltration. The recommendations are made in three categories: residential street and parking lots, lot development, and conservation of natural areas.
Ironically, local development rules, often based on outdated assumptions, prohibit the use of many principles. To help foster change, the principles have been used as the focal point in stakeholder roundtables conducted in the central Rappahannock watershed in Virginia, and in Cecil and Frederick counties in Maryland.
They will also be used for stakeholder roundtables by the new Builders for the Bay Program.
The principles are:
Residential Streets & Parking Lots
- Design residential streets for the minimum required pavement width needed to support travel, on-street parking, and emergency, maintenance and service vehicle access. These widths should be based on traffic volume. (Streets are the largest source of impervious cover in most subdivisions.)
- Reduce the total length of residential streets by examining alternative street layouts to determine the best option for increasing the number of homes per unity length. (Subdivisions often include longer roads than are needed to serve the number of homes.)
- Wherever possible, residential street right-of-way widths should reflect the minimum required to accommodate travel, sidewalks and vegetated open channels. Utilities and storm drains should be located within the pavement section of the right-of-way wherever feasible. (Wider than necessary rights-of-ways often result in more land clearing, and can impede more compact design.)
- Minimize the number of residential cul-de-sacs and incorporate landscaped areas to reduce their impervious cover. The radius of cul-de-sacs should be the minimum required to accommodate emergency and maintenance vehicles. Alternative turnarounds should be considered.
- Where density, topography, soils and slope permit, vegetated open channels should be used in the street right-of-way to convey and treat stormwater runoff. (This can remove more pollution by infiltration and filtering and is usually less expensive than curb and gutter stormwater systems.)
- The required parking ratio governing a particular land use or activity should be enforced as both a maximum and a minimum to curb excess parking construction. Existing parking ratios should be reviewed for conformance, taking into account local and national experience to see if lower ratios are warranted and feasible. (Most community parking codes are outdated and result in far more parking spaces being constructed than are actually needed).
- Parking codes should be revised to lower parking requirements where mass transit is available or enforceable shared parking arrangements are made. (Shared parking allows adjacent land uses to share parking lots if peak parking demands occur at different times of the week.)
- Reduce the overall imperviousness associated with large scale parking lots by providing compact car spaces, minimizing stall dimensions, incorporating efficient parking lanes and using pervious materials in the spillover parking areas where possible.
- Provide meaningful incentives to encourage structured and shared parking to make it more economically viable.
- Wherever possible, provide stormwater treatment for parking lot runoff using bioretention areas, filter strips, and/or other practices that can be integrated into required landscaping areas and traffic islands.
- Advocate open space design subdivisions incorporating smaller lot sizes to minimize total impervious area, reduce total construction costs, conserve natural areas, provide community recreational space and promote watershed protection. (By clustering homes onto a small area of the overall site, more open space is available for other uses.)
- Relax side yard setbacks and allow narrower frontages to reduce total road length in the community and overall site imperviousness. Relax front setback requirements to minimize driveway lengths and reduce overall lot imperviousness.
- Promote more flexible design standards for residential subdivision sidewalks. Where practical, consider locating sidewalks on only one side of the street and provide common walkways.
- Reduce overall lot imperviousness by promoting alternative driveway surfaces and shared driveways that connect two or more homes together.
- Clearly specify how community open space will be managed and designate a sustainable legal entity responsible for managing both natural and recreational open space.
- Direct rooftop runoff to pervious areas such as yards, open channels or vegetated areas and avoid routing rooftop runoff to the roadway and stormwater conveyance system.
Conservation of Natural Areas
- Create a variable width, naturally vegetated buffer system along all perennial streams that also encompasses critical environmental features such as the 100-year flood plain, steep slopes and freshwater wetlands.
- The riparian stream buffer should be preserved or restored with native vegetation. The buffer system should be maintained through the plan review, delineation, construction and post-development stages.
- The clearing and grading of forests and native vegetation at a site should be limited to the minimum amount needed to build lots, allow access and provide fire protection. A fixed portion of any community open space should be managed as protected green space in a consolidated manner. (Most communities allow the entire site to be cleared, increasing erosion during construction and disturbing natural hydrology.)
- Conserve trees and other vegetation at each site by planting additional vegetation, clustering tree areas, and conserving native vegetation. Wherever practical, incorporate trees into community open space, street rights-of-way, parking lot islands, and other landscaped areas. (Maintaining trees contributes to environmental quality and increases property values.)
- Incentives and flexibility should be encouraged to promote the conservation of stream buffers, forests, meadows, and other areas of environmental value. In addition, off-site mitigation should be encouraged where it is consistent with locally adopted watershed plans.
- New stormwater outfalls should not discharge unmanaged stormwater into jurisdictional wetlands, sole-source aquifers or sensitive areas.
For information about the principles, visit the Center for Watershed Protection’s web site at www.cwp.org